Liquid resins that are curably set into solid form in the field of automobile body repair. Similar resins are also used in marine applications.
Auto body fillers, marine fillers, and like products constitute a blend of uncured polyster resin, a cobalt accelerator and one or more fillers such as talc, titanium dioxide, glass microspheres, glass fibers and the like. Conventionally, the resin is packaged in a can and a separate smaller container of catalyst is provided for addition thereto. In preparation for use, a predetermined amount of resin is deposited on a clean, flat mixing surface or in a separate mixing container. The catalyst is then added in correct proportion to the amount of resin used.
The catalyst may be an oxidizing agent such as methyl ethyl ketone (MEK) peroxide or benzoyl peroxide that is usually supplied as a liquid in a small bottle or tube. Alternatively, the catalyst may be in the form of a paste stored in a squeeze tube. In the case of the liquid, added drops of catalyst are counted whereas in the paste form, a squeezed out ribbon of catalyst is measured to ensure that a correct proportion of catalyst is added to the resin. Both are manually mixed to obtain a uniform blend. The product is then applied to a work surface such as a dent in an automobile body and is smoothed to an appropriate contour in the few minutes available to a user before the resin polymerizes to a state where it cannot be worked.
Adequate ventilation is essential to avoid the harmful effects of volatile styrene monomer which is a toxic component in polyester resin. Although industrial health standards may be observed in well organized workshops, it is not likely that independent users would take the time or trouble to observe proper safety precautions in terms of adequate ventilation. The health of such users is therefore at risk.
Accurate control of the resin-catalyst ratio is important to achieve maximum working time of the blended resin as well as optimum strength in the hardened product. Thus, a distraction may easily lead to error when counting drops of catalyst which may result in a poor product. Extensive reworking may even be required resulting in wasted time and materials as a consequence of an incorrect ratio of resin and catalyst.
Mixing the catalyst and resin under aerobic conditions results in air bubbles that are entrained in the mixed product. When the cured resin is worked as by filing and sanding, the bubbles appear as pinholes in the finished surface which requires the further application of a skin coat of body filler or putty to provide an acceptable finished surface suitable for painting.
Tools, surfaces and containers used in mixing the resin and catalyst require laborious cleaning prior to subsequent use or else they must be discarded after polymerization of the resin occurs. Either case entails an expense that is quite likely to be substantial in commercial use having regard to the fact that material quantities may only be mixed in small batches in view of a short available working time. This characteristic in particular indicates a need for a cost effective package system since small batch usage dictates large quantity production runs.
Some of the foregoing problems associated with volatile resins and catalysts have been addressed more or less successfully in the art of compartmented receptacles.
An example of a package having a plurality of compartments suitable for storing and mixing reactive substances is disclosed in U.S. Pat. No. 2,756,874 Erickson et al. In one embodiment, the package comprises a flattened plastic film tube having open ends that are heat sealed closed. The sealed tube is further closed off into a dual compartment bag by means of a fold arrangement placed transversely of the tube between the ends. This fold arrangement includes a resilient core member made from rope, cellulose matter, or the like that extends transversely across the tube along one exterior side. The tube walls are wrapped partially around the member so that the inside surfaces of both walls come into contact. A flexible clamp engages the tube walls and grips same against the core member to effect an openable seal between compartments. Means are provided for filling the compartments, excluding air, and a relief strip is positioned between the walls and clamp to facilitate clamp removal without tearing the package.
Another example is a multiple chambered container made to separate liquid epoxy resins from a suitable hardener until the epoxy is to be used which is disclosed in U.S. Pat. No. 2,916,197 Detrie et al. The peripheral edges of a plastic bag are heat sealed shut and respective epoxy and hardener chambers are separated by one of a variety of internal dividing means that include a heat seal, a thin membrane, an adhesive, or a pair of opposed mating closure members. The epoxy and hardener mix when the dividing means are breached and the bag is kneaded. The bag contents are subsequently dispensed through a corner of the bag which is cut away.
Still another example appears in U.S. Pat. No. 3,462,070 Corella which discloses a dual compartment flexible bag fabricated from tubular, heat sealable plastic film. An openable closure is disposed across the tube intermediate both open ends. Two compartments are thus formed into which a separate reactive product is added followed by closure of the open ends as by heat sealing across the tube. At least one fold in the opposing side walls of the tube is lightly heat sealable to form the openable closure which is opened to mix the reactive products. Pulling the sealed tube ends in opposite directions straightens the fold by breaking an outer light heat seal which is then followed by squeezing one compartment to pressurize same. As a result, an inner light heat seal is broken and the closure is opened.
The bags of Erickson et al, Detrie et al and Corella are discarded after initial use and are intended to be produced in large quantities. Economy of manufacture is therefore an important criterion.
However, the disclosure in Erickson et al of an openable closure comprising a core member, a removable clamp and a relief strip which is added to the principal structure of a dual compartment flat bag appears to be greater in cost than the bag per se. The absence of a cost effective package is therefore clearly apparent.
The disclosure in Detrie et al of internal dividing or a pair of opposed mating closure members also indicates a relatively expensive bag structure that is not cost effective.
Similarly in Corella, the openable closure that requires lightly heat sealing a plurality of folded layers in each bag for about five seconds is a costly process by virtue of excessive machine time that results in an unnecessarily expensive disposable bag. Additional cost is incurred as a result of required extra adhesive when laminated plastic film is used.
Another shortcoming in the aforenoted prior art relates to the common teaching of breaching a barrier in a two compartment package and mixing the respective components thereof in both compartments. This is unsuitable when the mixing ratio of the respective components is disproportionate, resulting in loss of process control for varying reaction temperatures and desired hardening times.
Neither Erickson et al nor Corella refer to laminated films, only single layer films being disclosed, whereas laminates are necessary in packaging requiring toughness, an effective vapor barrier and heat sealability.
Common to the aforenoted prior art is the teaching of a seal between adjacent compartments that completely traverses the package. The extra length of such a seal increases the probability of premature leakage between compartments.
Still another shortcoming in the prior art are the "weak bonds" disclosed in Corella which will not function in the presence of polyster resin that attacks the laminate bond and leads to delamination. Also, since laminated plastic films cannot be heat sealed on their outer surface, Corella's folded layers require adhesive as noted hereinabove.